It is proposed to study mechanisms underlying the reduced antitumor activity of C. parvum-PEC in whole body irradiated animals. We also propose to extend our investigations into the observed stimulation of the effective T cell response to tumor by animals treated with C. parvum. Coupled with this work, we are developing techniques to separate and identify the host cell infiltrates of solid tumors. These studies are aimed at making functional assessments of the properties of such cells in relation to extra-tumoral cells of the same type. Finally, we plan to study the interactions between C. parvum and agents that modify T cell responses, in vivo.